Receptors for the Fc portion of immunoglobulin molecules (FcR) present on leukocyte cell membrane... more Receptors for the Fc portion of immunoglobulin molecules (FcR) present on leukocyte cell membranes mediate a large number of cellular responses that are very important in host defense. Cross-linking of FcR by immune complexes leads to functions such as phagocytosis, cell cytotoxicity, production and secretion of inflammatory mediators, and modulation of the immune response.
Human papillomavirus infection is associated with cervical cancer. The E6 and E7 papillomavirus p... more Human papillomavirus infection is associated with cervical cancer. The E6 and E7 papillomavirus proteins are normally required for the maintenance of the malignant phenotype. Expression of these proteins in infected cells is negatively regulated by the binding of the papilloma E2 protein to the long terminal control region of the papilloma virus genome. The E2 protein can also promote cell arrest and apoptosis in HeLa cells. Therefore, it is clear that this protein has the potential of inhibiting the malignant phenotype. Because, anticancer vaccines based in vaccinia viruses have recently been shown to be an effective way to treat and to eradicate tumors, a recombinant vaccinia virus expressing the E2 gene of bovine papilloma virus (Modified Vaccinia Ankara, MVA E2) was created, to explore further the antitumor potential of the E2 protein. A series of rabbits, containing the VX2 transplantable papilloma carcinoma, were treated with MVA E2. An impressive tumor regression, up to a complete disappearance of tumor, was observed in most animals (80%). In contrast, very little or no regression was detected if the normal vaccinia virus was used. Lymphocytes isolated from MVA E2-treated rabbits did not show cytotoxic activity against tumor cells. However, in these animals a humoral immune response against tumor cells was observed. These antitumor antibodies were capable of activating macrophages to destroy tumor cells efficiently. These data indicate that injecting the MVA E2 recombinant vaccinia virus directly into the tumor results in a robust and long-lasting tumor regression. Data also suggest that antitumor antibodies are responsible, at least in part, for eliminating tumors by activating macrophage antibody-dependent cytotoxicity.
Various hemocyte cell types have been described in invertebrates, but for most species a function... more Various hemocyte cell types have been described in invertebrates, but for most species a functional characterization of different hemocyte cell types is still lacking. In order to characterize some immunological properties of mussel (Mytilus galloprovincialis) hemocytes, cells were separated by flow cytometry and their capacity for phagocytosis, production of reactive oxygen species (ROS), and production of nitric oxide (NO), was examined. Phosphatidylinositol 3-kinase (PI 3-K), protein kinase C (PKC), and extracellular signal-regulated kinase (ERK) inhibitors were also used to biochemically characterize these cell responses. Four morphologically distinct subpopulations, designated R1–R4, were detected. R1, R2, and R3 cells presented different levels of phagocytosis towards zymosan, latex beads, and two bacteria species. Similarly, R1 to R3, but not R4, cells produced ROS, while all subpopulations produced NO, in response to zymosan. Internalization of all phagocytic targets was blocked by PI 3-K inhibition. In addition, internalization of latex particles, but not of bacteria, was partially blocked by PKC or ERK inhibition. Interestingly, phagocytosis of zymosan was impaired by PKC, or ERK inhibitors, only in R2 cells. Zymosan-induced ROS production was blocked by PI 3-K inhibition, but not by PKC, or ERK inhibition. In addition, zymosan-stimulated NO production was affected by PI 3-K inhibition in R1 and R2, but not in R3 or R4 cells. NO production in all cell types was unaffected by PKC inhibition, but ERK inhibition blocked it in R2 cells. These data reveal the existence of profound functional and biochemical differences in mussel hemocytes and indicate that M. galloprovincialis hemocytes are specialized cells fulfilling specific tasks in the context of host defense.
The molecular mechanism involved in Fc receptor-mediated phagocytosis in the different cell types... more The molecular mechanism involved in Fc receptor-mediated phagocytosis in the different cell types of the immune system is still poorly defined. We investigated the role of phosphatidylinositol 3-kinase (PI 3-K) and extracellular signal-regulated kinase (ERK) in phagocytosis by monocytes and by monocyte-differentiated macrophages. Peripheral blood monocytes and monocytic cells (THP-1 cell line) were able to ingest IgG-coated erythrocytes in the absence of additional stimulus. Phagocytosis by these cells was not blocked by wortmannin and LY294002, specific inhibitors of PI 3-K, or by PD98059, a specific MEK/ERK inhibitor. However, upon differentiation of THP-1 monocytes to macrophages, through treatment with retinoic acid and interferon-␥ (IFN-␥), wortmannin and PD98059 blocked Fc receptor-mediated phagocytosis efficiently. Inhibition of phagocytosis by PD98059 was observed after 24 h of IFN-␥ treatment, whereas wortmannin could inhibit phagocytosis only after 48 h of IFN-␥ treatment. Additionally, phagocytosis of IgG-coated erythrocytes by neutrophils, a more efficient phagocyte, was inhibited by wortmannin and PD98059. Neutrophils and monocyte-differentiated macrophages presented significantly more efficient phagocytosis than monocytes upon PMA stimulation. Taken together, these results indicate that poorly phagocytic leukocytes, such as monocytes, do not require PI 3-K and ERK for phagocytosis. Upon differentiation into macrophages, however, ERK first and PI 3-K second are recruited for regulation of phagocytosis. In addition, our data support the idea that professional phagocytes require ERK and PI 3-K for efficient phagocytosis. J. Leukoc. Biol. 72: 107-114; 2002.
Phagocytosis is the process whereby cells engulf large particles, usually over 0.5 m in diameter.... more Phagocytosis is the process whereby cells engulf large particles, usually over 0.5 m in diameter. Phagocytosis is triggered by the interaction of opsonins that cover the particle to be internalized with specific receptors on the surface of the phagocyte. The best-studied phagocytic receptors include the Fc receptors (FcR) that bind to the Fc portion of immunoglobulins. Cross-linking of FcR on the phagocyte initiates a variety of signals, which lead through the reorganization of the actin cytoskeleton, and membrane remodeling, to the formation of the phagosome. From recent data, it is becoming clear that FcR-mediated phagocytosis occurs as a series of steps that are regulated in a nonlinear manner and that signaling for phagocytosis does not terminate when the phagosome is formed. Several lipid molecules localize around the nascent phagosome and function as initiators of important signaling pathways for the late stages of phagolysosome formation. In addition, the use of particular signaling molecules may change for different receptors and may also vary depending on the activation or differentiation state of the cell. This review focuses on this new information and presents a model of our present understanding of the signal transduction events that regulate phagocytosis mediated by FcR.
This paper presents detailed numerical calculations of the dielectrophoretic force in traps desig... more This paper presents detailed numerical calculations of the dielectrophoretic force in traps designed for single-cell trapping. A trap with eight planar electrodes is studied for spherical and ellipsoidal particles using the boundary element method (BEM). Multipolar approximations of orders one to three are compared with the full Maxwell stress tensor (MST) calculation of the electrical force on spherical particles. Ellipsoidal particles are also studied, but in their case only the dipolar approximation is available for comparison with the MST solution. The results show that a small number of multipolar terms need to be considered in order to obtain accurate results for spheres, even in the proximity of the electrodes, and that the full MST calculation is only required in the study of nonspherical particles.
Receptors for the Fc portion of immunoglobulin molecules (FcR) present on leukocyte cell membrane... more Receptors for the Fc portion of immunoglobulin molecules (FcR) present on leukocyte cell membranes mediate a large number of cellular responses that are very important in host defense. Cross-linking of FcR by immune complexes leads to functions such as phagocytosis, cell cytotoxicity, production and secretion of inflammatory mediators, and modulation of the immune response.
Human papillomavirus infection is associated with cervical cancer. The E6 and E7 papillomavirus p... more Human papillomavirus infection is associated with cervical cancer. The E6 and E7 papillomavirus proteins are normally required for the maintenance of the malignant phenotype. Expression of these proteins in infected cells is negatively regulated by the binding of the papilloma E2 protein to the long terminal control region of the papilloma virus genome. The E2 protein can also promote cell arrest and apoptosis in HeLa cells. Therefore, it is clear that this protein has the potential of inhibiting the malignant phenotype. Because, anticancer vaccines based in vaccinia viruses have recently been shown to be an effective way to treat and to eradicate tumors, a recombinant vaccinia virus expressing the E2 gene of bovine papilloma virus (Modified Vaccinia Ankara, MVA E2) was created, to explore further the antitumor potential of the E2 protein. A series of rabbits, containing the VX2 transplantable papilloma carcinoma, were treated with MVA E2. An impressive tumor regression, up to a complete disappearance of tumor, was observed in most animals (80%). In contrast, very little or no regression was detected if the normal vaccinia virus was used. Lymphocytes isolated from MVA E2-treated rabbits did not show cytotoxic activity against tumor cells. However, in these animals a humoral immune response against tumor cells was observed. These antitumor antibodies were capable of activating macrophages to destroy tumor cells efficiently. These data indicate that injecting the MVA E2 recombinant vaccinia virus directly into the tumor results in a robust and long-lasting tumor regression. Data also suggest that antitumor antibodies are responsible, at least in part, for eliminating tumors by activating macrophage antibody-dependent cytotoxicity.
Various hemocyte cell types have been described in invertebrates, but for most species a function... more Various hemocyte cell types have been described in invertebrates, but for most species a functional characterization of different hemocyte cell types is still lacking. In order to characterize some immunological properties of mussel (Mytilus galloprovincialis) hemocytes, cells were separated by flow cytometry and their capacity for phagocytosis, production of reactive oxygen species (ROS), and production of nitric oxide (NO), was examined. Phosphatidylinositol 3-kinase (PI 3-K), protein kinase C (PKC), and extracellular signal-regulated kinase (ERK) inhibitors were also used to biochemically characterize these cell responses. Four morphologically distinct subpopulations, designated R1–R4, were detected. R1, R2, and R3 cells presented different levels of phagocytosis towards zymosan, latex beads, and two bacteria species. Similarly, R1 to R3, but not R4, cells produced ROS, while all subpopulations produced NO, in response to zymosan. Internalization of all phagocytic targets was blocked by PI 3-K inhibition. In addition, internalization of latex particles, but not of bacteria, was partially blocked by PKC or ERK inhibition. Interestingly, phagocytosis of zymosan was impaired by PKC, or ERK inhibitors, only in R2 cells. Zymosan-induced ROS production was blocked by PI 3-K inhibition, but not by PKC, or ERK inhibition. In addition, zymosan-stimulated NO production was affected by PI 3-K inhibition in R1 and R2, but not in R3 or R4 cells. NO production in all cell types was unaffected by PKC inhibition, but ERK inhibition blocked it in R2 cells. These data reveal the existence of profound functional and biochemical differences in mussel hemocytes and indicate that M. galloprovincialis hemocytes are specialized cells fulfilling specific tasks in the context of host defense.
The molecular mechanism involved in Fc receptor-mediated phagocytosis in the different cell types... more The molecular mechanism involved in Fc receptor-mediated phagocytosis in the different cell types of the immune system is still poorly defined. We investigated the role of phosphatidylinositol 3-kinase (PI 3-K) and extracellular signal-regulated kinase (ERK) in phagocytosis by monocytes and by monocyte-differentiated macrophages. Peripheral blood monocytes and monocytic cells (THP-1 cell line) were able to ingest IgG-coated erythrocytes in the absence of additional stimulus. Phagocytosis by these cells was not blocked by wortmannin and LY294002, specific inhibitors of PI 3-K, or by PD98059, a specific MEK/ERK inhibitor. However, upon differentiation of THP-1 monocytes to macrophages, through treatment with retinoic acid and interferon-␥ (IFN-␥), wortmannin and PD98059 blocked Fc receptor-mediated phagocytosis efficiently. Inhibition of phagocytosis by PD98059 was observed after 24 h of IFN-␥ treatment, whereas wortmannin could inhibit phagocytosis only after 48 h of IFN-␥ treatment. Additionally, phagocytosis of IgG-coated erythrocytes by neutrophils, a more efficient phagocyte, was inhibited by wortmannin and PD98059. Neutrophils and monocyte-differentiated macrophages presented significantly more efficient phagocytosis than monocytes upon PMA stimulation. Taken together, these results indicate that poorly phagocytic leukocytes, such as monocytes, do not require PI 3-K and ERK for phagocytosis. Upon differentiation into macrophages, however, ERK first and PI 3-K second are recruited for regulation of phagocytosis. In addition, our data support the idea that professional phagocytes require ERK and PI 3-K for efficient phagocytosis. J. Leukoc. Biol. 72: 107-114; 2002.
Phagocytosis is the process whereby cells engulf large particles, usually over 0.5 m in diameter.... more Phagocytosis is the process whereby cells engulf large particles, usually over 0.5 m in diameter. Phagocytosis is triggered by the interaction of opsonins that cover the particle to be internalized with specific receptors on the surface of the phagocyte. The best-studied phagocytic receptors include the Fc receptors (FcR) that bind to the Fc portion of immunoglobulins. Cross-linking of FcR on the phagocyte initiates a variety of signals, which lead through the reorganization of the actin cytoskeleton, and membrane remodeling, to the formation of the phagosome. From recent data, it is becoming clear that FcR-mediated phagocytosis occurs as a series of steps that are regulated in a nonlinear manner and that signaling for phagocytosis does not terminate when the phagosome is formed. Several lipid molecules localize around the nascent phagosome and function as initiators of important signaling pathways for the late stages of phagolysosome formation. In addition, the use of particular signaling molecules may change for different receptors and may also vary depending on the activation or differentiation state of the cell. This review focuses on this new information and presents a model of our present understanding of the signal transduction events that regulate phagocytosis mediated by FcR.
This paper presents detailed numerical calculations of the dielectrophoretic force in traps desig... more This paper presents detailed numerical calculations of the dielectrophoretic force in traps designed for single-cell trapping. A trap with eight planar electrodes is studied for spherical and ellipsoidal particles using the boundary element method (BEM). Multipolar approximations of orders one to three are compared with the full Maxwell stress tensor (MST) calculation of the electrical force on spherical particles. Ellipsoidal particles are also studied, but in their case only the dipolar approximation is available for comparison with the MST solution. The results show that a small number of multipolar terms need to be considered in order to obtain accurate results for spheres, even in the proximity of the electrodes, and that the full MST calculation is only required in the study of nonspherical particles.
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Papers by Carlos Rosales